The invention relates to a switch-over device for a filling station and to a gas filling station for filling a pressure container with a gas.
Compressed natural gas is gaining above all in importance as an alternative fuel for motor vehicles. In order to enable a satisfactory range for motor vehicles which are operated with natural gas and at the same time to keep the dimensions of the supply container in the motor vehicle within reasonable limits, these supply containers are typically filled up to pressures of about 200 bar with respect to a reference temperature of 15xc2x0 C. Filling methods and filling stations have been developed for this which enable a very simple and rapid filling of motor vehicles of this kindxe2x80x94comparable to filling with gasoline. A method of this kind and a gas filling station of this kind respectively are shown for example in EP-A-653 585 in detail.
Gas filling stations of this kind, by means of which mobile pressure containers such as e.g. the supply container of a gas-operated motor vehicle are filled with gas, typically comprise a stationary storage unit which is filled with compressed gas and a dispensing apparatus in order to connect the stationary storage unit to the mobile supply container, so that the gas can flow out of the storage unit into the mobile supply container.
In EP-A-653 585 it is proposed that the stationary storage unit comprises a plurality of, especially three, reservoirs. In the dispensing apparatus a switch-over device is provided by means of which one of the reservoirs can in each case be connected to the pressure line which leads to the pressure container to be filled. The switch-over device enables a switching over from one stationary reservoir to another stationary reservoir as source for the filling during a filling operation. Thus if during the filling the pressure difference between the stationary reservoir and the mobile supply container decreases, e.g. as a result of the increasing emptying of the stationary reservoir, to such an extent that the volume flow of the gas with respect to time becomes very low, then a switchover can be made to another reservoir without an interruption of the filling process, in order to ensure a rapid progress of the filling.
In accordance with EP-A-653 585 the mass flow of the gas dispensed is determined by measurement by means of a mass flow meter and the measured value is transmitted to a control apparatus. As soon as the control apparatus detects that the mass flow falls below a predeterminable threshold value during the filling, the control apparatus drives the switch-over device in such a manner that a switchover is made to a reservoir with higher pressure. Although this procedure has proven useful in practice, it is nevertheless relatively complex and cost intensive.
It is an object of the invention to propose a switch-over device which is as simple and economical as possible and which in particular enables a switching over from one reservoir of a filling station to another as soon as the mass flow falls below a threshold value. In addition, this switching over should be possible without interrupting the filling process for it.
Thus in accordance with the invention a switch-over device for a filling station is proposed which comprises at least a first and a second input for a fluid which is under pressure, an outlet for the fluid and flow connections via which each input can be connected to the outlet. A switch-over valve which has a valve body, which can be actuated by the fluid and which in its closure position closes off the flow connection between the second input and the outlet, is provided in the flow connection between the second input and the outlet. Control connections for the fluid are arranged in such a manner that the valve body of the switch-over valve is acted upon on the one side by the pressure of the fluid at the first input and on the other side by the pressure of the fluid at the outlet.
As long as the switch-over valve is in the closure position, fluid can flow only from the first input to the outlet of the switch-over device. If for example in a gas filling station the first input is connected to a first stationary reservoir and the outlet to the pressure container to be filled, then the fluid flows out of the first reservoir into the pressure container. As a result of the control connections the valve body of the switch-over valve is acted upon on the one side by the pressure of the fluid at the first input and on the other side by the pressure of the fluid at the outlet. The pressure difference which results from this holds the valve body of the switch-over valve in the closure position, so that the flow connection between the second input, which is for example connected to a second stationary reservoir, and the outlet is closed. If the pressure difference falls below a predeterminable threshold value, because for example on the one hand the pressure at the first input decreases and on the other hand the pressure at the outlet increases as a result of the pressure container, which is filled more and more, then the switch-over valve automatically switches into its open position and thereby opens the flow connection between the second input and the outlet. Now the fluid can flow from the second input, thus for example from the second stationary reservoir, to the outlet and then into the pressure container to be filled.
The threshold value of the pressure difference at which the switch-over valve switches can be predetermined in a simple way. For example the valve body can be subjected to a bias force by a correspondingly dimensioned spring. It is also possible to design the area of the valve body which is acted upon by the pressure of the fluid at the first input on the one hand and the area which is acted upon by the pressure of the fluid at the outlet on the other hand to be of different sizes in order thereby to predetermine the threshold value for the pressure difference. In principle all measures which are known per se are suitable in order to predetermine the threshold value for the pressure difference at which the switch-over valve switches.
The switch-over device in accordance with the invention thus has the property that it automatically opens the flow connection between the second input and the outlet as soon as the pressure difference between the first input and the outlet falls below a threshold value. It is in particular not necessary to determine measurement parameters such as e.g. the mass flow of the fluid and to cause the switching over through external drive means. This signifies a considerable reduction in the complexity of the apparatus and in the costs.
Especially in the case of gas filling stations there are applications, e.g. works-internal gas filling stations, in which it is not absolutely necessary to determine by measurement the amount of gas given off during the filling. In such applications the switch-over device in accordance with the invention enables a mass flow meter, such as for example a Coriolis measurement device, to be dispensed with entirely. Since these devices are particularly complicated, expensive and sensitive, costs can be saved to a considerable extent through the switch-over device in accordance with the invention.
In particular in regard to the application in gas filling stations, which frequently comprise at least three stationary reservoirs, the switch-over device preferably has n inputs for the fluid, with n=3, 4, 5, . . . , each of which can be connected via a flow connection to the outlet, wherein a further switch-over valve which has a valve body, which can be actuated by the fluid and which closes the flow connection between the n-th input and the outlet in its closure position, is in each case provided in the flow connection between the n-th input and the outlet, and wherein in each case flow connections for the fluid are arranged in such a manner that the valve body of this switch-over valve is acted upon on the one side by the pressure of the fluid at the (n-1)-st input and on the other side with the pressure of the fluid at the outlet.
In a manner analogous to that described above, the pressure difference between the (n-1)-st input and the outlet holds the switch-over valve which is provided between n-th input and the outlet in its closure position as long as this pressure difference is greater than a predeterminable threshold value. If the pressure difference falls below this threshold value, then the switch-over valve switches into the open position and thereby opens the flow connection between the n-th input, which is for example connected to an n-th reservoir, and the outlet. Now the fluid can flow from the n-th input to the outlet.
The switch-over device thus successively and automatically opens the flow connection between the next, for example the n-th, input and the outlet as soon as the pressure difference between the (n-1)-st input and the outlet falls below a threshold value.
Each switch-over valve preferably comprises a spring element which acts on and stresses the valve body of the switch-over valve, with setting means being provided in order to vary the stressing of the valve body which is caused by the spring element. Through this measure the pressure difference at which the switch-over valve switches from the closure into the open position can be predetermined in a particularly simple and reliable way.
Furthermore, for practical reasons, designs are preferred in which the respective flow connections, via which the inputs can be connected to the outlet, unite downstream from the switch-over valve or the switch-over valves respectively to form a common outlet line.
In a particularly preferred embodiment the switch-over device comprises a single-piece block at which all inputs and the outlet are provided, with all flow connections and all control connections being designed as bores in the single-piece block, and with bores furthermore being provided for the reception of each valve body. This single-piece block enables a particularly compact and space-saving design. In addition the single-piece design is advantageous in regard to leakage losses. The single-piece block with the bores furthermore brings about the advantage that lines and connection elements such as for example screw connections can largely be dispensed with. Through this the operating safety increases, since the risk of damage to lines or to connections between lines respectively is considerably reduced.
Furthermore, a pressure limiting valve which has a valve body which is arranged in a bore of the single-piece block in such a manner that it opens or closes the passage through the common outlet line depending on its position is advantageously provided. This pressure limiting valve serves for example in a gas filling station to terminate the filling process as soon as the final pressure has been reached in the pressure container to be filled.
It is also advantageous when the pressure limiting valve comprises a spring element which acts on and stresses the valve body of the pressure limiting valve, with means being provided in order to vary, in dependence on the temperature, the stressing of the valve body which is caused by the spring element. In gas filling it is usually the case that the permissible final pressure at which the filling is terminated depends on the ambient temperature. In gas-operated motor vehicles their supply container is typically filled up to a pressure of about 200 bar with respect to a reference temperature of 15xc2x0 C. If the filling takes place at an ambient temperature of less than 15xc2x0 C., then the final pressure at which the filling is terminated must amount to less than 200 bar in order to ensure that when the ambient temperature rises, an impermissibly large pressure does not arise in the supply container of the motor vehicle. On the contrary, at an ambient temperature of more than 15xc2x0 C. filling can take place up to a final pressure of more than 200 bar without the risk of too high a pressure in the supply container arising. Through the means for varying in dependence on the temperature the stressing of the valve body which is caused by the spring element, the pressure limiting valve automatically adapts the final pressure at which the filling is terminated to the ambient temperature or to the temperature of the gas respectively.
Furthermore, for safety reasons an electromagnetically actuatable blocking valve is preferably provided in the switch-over device for opening and closing the flow connections between the inputs and the outlet. There exists thereby the possibility of closing the outlet immediately by means of an electrical signal when for example a fault in the filling station is detected. This electrical signal can e.g. come from a control and monitoring device.
A further advantageous measure consists in providing a filter for filtering the fluid in the region of each input in order to avoid contamination.
Furthermore, it is advantageous to provide a non-return valve in each flow connection between one of the inputs and the outlet. In this at least those non-return valves which are provided in the flow connections between the first to the (n-1)-st input and the outlet preferably comprise in each case setting means by which the pressure difference at which the respective non-return valve opens can be set. Through this measure namely, the pressure difference at which the switch-over valve switches from the closure into the open position can also be set.
Furthermore, a gas filling station for filling a pressure container with a gas is proposed by the invention which comprises at least two reservoirs for the gas and a dispensing apparatus in order to fill the gas from the reservoirs into the pressure container. A switch-over device in accordance with the invention is provided in this gas filling station, with each of the reservoirs being connected to an input of the switch-over device and the outlet of the switch-over device being connectable to the pressure container.
A gas filling station of this kind has the advantage that the switching over from one reservoir to the next one takes place automatically and without the determination of the mass flow being required for this. This signifies a considerable reduction of the complexity and the costs in comparison with known gas filling stations.
In the following the invention will be explained in more detail with reference to exemplary embodiments and with reference to the drawings.